The incidence of pediatric inflammatory bowel disease (IBD) is increasing worldwide. Ecological studies show higher incidence in regions at higher latitude or lower ambient ultraviolet radiation; individual-level associations with sun exposure have not been assessed.
We recruited children (0–17 years) with IBD from two large hospitals in Melbourne, Australia. Control participants were recruited from the day surgery unit of one of the same hospitals. Questionnaires provided data on demographics, past sun exposure, the likelihood of sunburn (skin sensitivity) or tanning following sun exposure, use of sun protection, physical activity, and parental smoking and education. Grandparent ancestry was used to determine participant ethnicity. Cases and controls were matched on age and sex. We used conditional logistic regression to test the association between being an IBD case and past sun exposure at different ages, adjusted for a range of other factors.
After matching, n = 99 cases and n = 396 controls were included in the analysis. In multivariable analysis, for each 10 min increment in leisure-time sun exposure in summer or winter there was a linear 6% reduction in the odds of having IBD (p = 0.002). Results were similar in sensitivity analyses including only the most recently diagnosed cases, only Caucasian cases and controls, only those with symptom onset within the year prior to study entry, or additionally adjusted for age or physical activity.
Higher sun exposure in the previous summer or winter was associated with a reduced risk of having IBD. There are plausible pathways that could mediate this effect.
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*National Centre for Epidemiology and Population Health, Research School of Population Health, The Australian National University, Canberra, Australia
†Murdoch Childrens Research Institute, Melbourne, Australia
‡Department of Paediatrics, University of Melbourne, Melbourne, Australia
§Deakin University, Burwood, Victoria, Australia.
Address correspondence and reprint requests to Prof. Robyn M. Lucas, National Centre for Epidemiology and Population Health, Research School of Population Health, Building 62, Australian National University, Canberra, Australia 2600 (e-mail: firstname.lastname@example.org).
Received 5 November, 2018
Accepted 22 April, 2019
PAID Consortium: Pediatric AutoImmune Disease Consortium
Conflict of interest: the authors declare no conflicts of interest
Funding: This work was supported by funding by the National Health and Medical Research Council of Australia through Senior Research Fellowships for RM Lucas, A-L Ponsonby, and C Kirkwood.
Author Contributions: ALP, JAE, and CDK conceived the idea and designed the study. CDK and the PAID consortium were responsible for acquisition of the data. RML, EAH, AP and ALP analysed and interpreted the data. RML and EAH drafted the paper; all authors were involved in revising the paper critically for important intellectual content. All authors read and approved the final version of the manuscript to be submitted.
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